The present invention relates, in general, to tongs for handling hot objects, and in particular, to a new and useful apparatus which has easily interchangeable jaws which are constructed specifically for grasping hot investment molds or flasks which are either of the oval type or cylindrical ring type.
The use of investment casting technology in the field of dentistry and jewelry, is well-known and well-developed. A pattern made of wax or meltable synthetic material is prepared. This pattern substantially corresponds to the piece of jewelry or dental hardware to be cast in metal. The pattern is set on a base using sprues and then a flask, traditionally a cylinder of metal having opposite open ends, is set around the pattern and onto the base. An investment solution is then carefully poured into the flask with appropriate safeguards to avoid the formation of bubbles around the pattern. The investment is allowed to set. The base is then removed and the investment is heated to melt away the pattern and leave a void on the inside of the investment. This void is the shape of the jewelry piece or dental hardware.
Using appropriate metal casting equipment, the void is then filled with metal, for example, gold or other precious or nonprecious metal.
Once the metal has cooled and set, the investment is broken away revealing the metal part which can then be further processed.
Furnace temperatures are in the neighborhood of 900.degree. F. to 2100.degree. F. and the investment is also at this temperature during much of the process. Tongs for use in holding the conventional cylindrical investments are known and are made of metal. See, for example, the catalogs to Kerr Sybron and Neycraft which carry one piece metal tongs. These tongs are very short and generally require the operator to be within 12 inches of the hot casting mold. Heavy gloves must be used or else the operator would quickly burn his or her hand. Even with heavy gloves, eventually the gloves become too hot because of the heat radiating from the furnace and mold, and must be removed and allowed to cool. Although longer tongs might be utilized, these can only be operated using both hands and the operator would have difficulty holding and manipulating the hot investment mold using such tongs. Often, a second operator is required in order to load the molds into the casting machines while the operator controls a torch forming part of the casting machine. Tongs are known which have a handle with trigger, a long shaft and jaws that can be closed by pressing the trigger. These are generally used in a grocery store environment. U.S. Pat. No. 3,527,492 discloses an instrument which goes by the commercial name "EZ Reacher". The instrument is used to pick up trash and has a trigger. While rubber or metal tips can be provided on the jaws of this instrument, the instrument is too flexible and cannot be used to grasp and hold items as heavy as casting molds. The tongs are designed for maximum load of about 4 to 12 ounces and are not strong enough or specially designed to be heat resistant.
Since many of the furnaces, casting machines and other equipment used during the casting of jewelry and dental parts, utilize electricity, it would also be advantageous to utilize tongs which are not electrically conducting. This is not the case for the tongs normally used in the field of jewelry and dental casting which, as noted above, are made of a single piece of metal which is inherently electrically conductive.
The traditional cylindrical investment molds have also been partly replaced by oval molds introduced by the co-inventor of the present application and others. There is no currently available mechanism for conveniently and accurately grasping oval casting molds.